Glutathione (GSH), in its reduced form, is a tripeptide of the formula: .gamma.-Glu-Cys-Gly. Reduced glutathione has a central role in maintaining the redox condition in cells and is also an essential substrate for glutathione S-transferase (GST). GST exists in mammals as a superfamily of isoenzymes which regulate the metabolism and detoxification of foreign substances introduced into cells. In general, GST can facilitate detoxification of foreign substances by a number of mechanisms and can also convert certain precursors into toxic substances.